How often? About half the time I used my bike to actually get places. As to weight, it is negligible. Most of my bikes weight around 30# none lighter than 24#, a kickstand is inconsequential. Really convenient when I forget my lock, and the brewery lets me roll it into their vestibule for safe keeping.

As to a real world example of where you can't use random objects to lean: my college was very adamant about bikes not being leaned against buildings and trees, and Facilities would drive around removing them on a regular basis, holding them for a $20 or so "ransom", aka parking ticket. I'm not about to leave it lying on the ground, as if everyone did that you would (and occasionally did) wind up with a pile of bikes to pick yours out of, so when racks were full it got stood up with a lock ran through the back tire so someone couldn't ride off.